Normal air diffusion reduces tire pressure over time. The natural state of tires is under inflated. Accordingly, drivers must repeatedly act to maintain tire pressures or they will see reduced fuel economy, tire life and reduced vehicle braking and handling performance. Tire Pressure Monitoring Systems have been proposed to warn drivers when tire pressure is significantly low. Such systems, however, remain dependent upon the driver taking remedial action when warned to re-inflate a tire to recommended pressure. It is a desirable, therefore, to incorporate a self-inflating feature within a tire that will self-inflate the tire in order to compensate for any reduction in tire pressure over time without the need for driver intervention.
One type of self inflating tire feature is a peristaltic pump assembly. If the pump is annular or 360 degrees in length, it will not be bidirectional unless there is additional valving. The use of 2 180 degree pumps allow the system to be bidrectional. This is because only one pump works when the tire rotates in one direction, and the other pump works when the tire rotates in the opposite direction.
Thus it is desired to have a simple pump design that is bidirectional and can pump 360 degrees without the need for complicated valving.